The present invention relates to producing an ultrasound image using line based image reconstruction.
Ultrasound imaging has become important for the medical diagnosis and understanding of stages of cardiovascular diseases such as strokes and heart attacks. Because of the rapid motions of a beating heart and other rapidly moving anatomy, special techniques have been designed to capture images rapidly to provide an accurate visual representation of rapidly moving anatomy. Of particular interest are the valves of the heart and the precise motions of the heart muscle wall. Also of interest are high quality representations and analyses of blood flow patterns.
The electro cardiogram (or “ECG”, and sometimes referred to as “EKG”) is a technique used to monitor electrical signals originating from the heart during its movement. Electrical signals originating from the heart may be detected at the surface of the skin in the vicinity of the heart. The ECG signal can be used to track the cycle of heart function. Various “ECG gating” or “ECG synchronization” techniques have been developed to improve ultrasound image acquisition by making use of simultaneously acquired ECG signals to coordinate timing of image acquisition relative to the cardiac cycle.
Ultrasound ECG techniques have focused on the acquisition of complete image frames at specific time intervals on the ECG wave form. By ‘triggering’ the start of ultrasound frame acquisition at a specified time relative to each heart beat, and acquiring image after image at the same point in the cardiac cycle, systems can effectively freeze the motion of the heart using a “strobing” principle. Systems also begin image acquisition at a specified interval from a standard point in the ECG wave form, such that two sets of moving heart images can be synchronized and compared, beginning from the same point in the cardiac cycle. ECG gating on a frame by frame basis is a good technique so long as the acquisition time for any given frame is relatively short compared to the movements depicted. A good analogy is a photograph with a short exposure time. The faster the motion, the shorter the exposure time that is required to accurately capture the structure in motion. Too long an exposure time results in a distorted image.
ECG based frame reordering has also been attempted to visualize rapidly moving anatomy. In a frame based reordering technique, a moderate increase in frame rate can be achieved by collecting data frames, and reordering the data frames by comparing the start time of each frame acquisition to the ECG signal. Frames can then be replayed at a faster rate. However, this technique does not yield a true representation of the rapidly moving anatomy because the finite time required to acquire a frame causes data overlap between frames. Thus each “stop motion” frame may not have complete time independence.
These existing ECG based imaging techniques have worked adequately well in the area of human echocardiography, the use of ultrasound for examination of the heart, but are insufficient for higher frame rate applications such as imaging rapidly moving structures in small animals. For example, the heart rate of a small animal, such as a mouse, is significantly faster than the heart rate of a human. The assumption that a frame acquisition is relatively instantaneous no longer holds true at faster rates, therefore gating ultrasound acquisition on a frame basis is not useful for imaging such rapidly moving anatomy.